Terrestrial mobile radiocommunication systems, namely the European system UMTS (Universal Mobile Telecommunication System), the development thereof HSPA (High Speed Packet Access), and the American system CDMA2000, as well as the developments thereof, are already operational and offer so-called third generation, or 3G, broadband services with up to 1 Mbits/s.
Standards for the new generation, so-called fourth generation or 4G, systems, such as LTE (Long Term Evolution 3GPP Technology) and WIMAX IEEE 802.16 (Worldwide Interoperability for Microwave Access), are under development and offer services at even higher rates. Deployment of such 4G systems is planned to start in 2010.
All of these third and fourth generation systems can additionally include a satellite-based spatial component intended to complete and cover, as so-called satellite umbrella cells, the coverage of much smaller terrestrial cells which form the terrestrial component and are deployed namely in urban areas where the high field level thereof ensures good quality service and where population density is sufficient for them to be cost-effective, so that they are compatible with the radio propagation conditions of the urban environment which are difficult for satellites.
In order to increase the capacity of such hybrid telecommunication systems, the gain provided by frequency reuse within a band of terrestrial frequencies allocated to the terrestrial component is increased by a decrease in size of the terrestrial cells.
Similarly, the size of the umbrella cells must be decreased so as to adapt the granularity of the set of umbrella cells to the granularity of the set of terrestrial cells included in the umbrella cell, and to increase the efficiency of frequency reuse operated within a satellite frequency band allocated to the satellite component.
Regardless of the fact that the allocated band of terrestrial frequencies and the allocated band of satellite frequencies can be identical, partially identical, or distinct, interferences between terrestrial cells and satellite umbrella cells will occur due to instability of positioning or shape of the satellite beam(s) at the origin of the umbrella cells with respect to the terrestrial cells, with positioning or shape instability having various causes such as the antennas' sensitivity to variations in temperature, or the imperfection of attitude control of the satellite platform.